TLALMANALCO, Mexico — Investigators dug and probed at a mass grave site through the night searching for more bodies and any connection to the mysterious disappearance of 12 young revelers from a bar in an upscale area of Mexico City three months ago.

Seven corpses covered in lime and sand were found Thursday in a shallow grave on a ranch in Tlalmanalco east of the capital, a federal agent said. By evening, more backhoes were seen entering the property as excavators continued the search.

Mexico City prosecutor Rodolfo Rios, who confirmed the discovery of seven bodies, said DNA tests would take two to three days to determine if the remains belonged to the young bar-goers. They vanished from the after-hours Heaven club at midday May 26, just a block from the leafy Paseo de Reforma, the capital’s equivalent of Paris’ Champs-￉lys￩es.

The bizarre disappearance resonated across the city of 9 million people because many had come to believe it was an oasis from Mexico’s cartels and drug violence.

The mass abduction of 12 mirrored crimes in drug-trafficking hot spots such as the western state of Guerrero, where 20 Mexican men from neighboring Michoacan disappeared, only to be found in a mass grave, or in Nuevo Leon, where the bodies of 17 kidnapped musicians were found at the bottom of a well.

Mexico City officials have insisted since the Heaven kidnapping that large drug cartels do not operate in the capital. But the case has been a political liability, with local polls saying the public is overwhelmingly opposed to how the administration of Mayor Miguel Mancera has handled the investigation.

The federal agent at the ranch, who agreed to tell about the search only if not quoted by name because he was not authorized to discuss details of the case, said clothing found with the corpses made it “90 percent sure” that officials had found the Heaven victims.

Authorities kept more than a mile perimeter around the excavation site on a hilly ranch known as La Negra, where federal police and attorney general’s trucks and large white vans could be seen. The private property next to Rancho La Mesa Ecological Park is walled and surrounded by oak and pine trees.

The federal Attorney General’s Office said agents had received information about possible illegal weapons on the property and obtained a search warrant. When they started looking around, they discovered the grave.

“They found a home that looked like a safe house,” Attorney General Jesus Murillo Karam told reporters. “We were operating under the belief it was a weapons case.”

Later, some of the relatives showed up on the property being excavated, crying and covering their faces from the media.

“We have had three months with this anxiety,” Maria Teresa Ramos, grandmother of Jerzy Ortiz, one of the missing, told Milenio television. “We are dying every day, little by little.”

Prosecutors have said the abductions from the Heaven bar were linked to a dispute between street gangs that control local drug sales in the capital’s nightclubs and bars.

They say the gangs are based in Mexico City’s dangerous Tepito neighborhood, where most of the missing lived. The families insist the missing young people were not involved in drug trafficking.

Surveillance cameras showed several cars pulling up to the bar at midday and taking the victims away. A witness who escaped told authorities that a bar manager had ordered the music turned off, told patrons that authorities were about to raid the establishment and ordered those inside to leave.

So far, five people have been detained in the Heaven case, including club owner Ernesto Espinosa Lobo, known as “The Wolf,” who has been charged with kidnapping. Among the arrested are another bar owner, a driver and a security guard. A fifth, Jose de Jesus Carmona, 32, is under arrest pending charges.

One suspect is still a fugitive.

In another element of the case that is reminiscent of cartel warfare, one of the owners of the Heaven bar, Dax Rodriguez Ledezma, fled authorities only to turn up dead, his body dumped and burned in a rural area with that of his girlfriend and another friend.